Sensitized photoconductive compositions comprising polymethine dyes containing a mercapto group



United States Patent 3,047,384 SENSITHZED PHOTQCONDUCTWE CQMPOSI- TIONS COMPRISING POLYMETHlNE DYES CUNTAINING A MERCAPTQ GROUP Jean E. Jones and Paul H. Stewart, Rochester, N.Y., as-

signors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Apr. 9, 1959, Ser. No. 8%,156 13 Claims. (Cl. 96-4) This invention relates to sensitized photoconductive compositions and layers comprising zinc oxide which are particularly useful in the document copying field.

This application is a continuation-in-part of US. application Serial No. 630,462, filed December 26, 1956, by Paul H. Stewart (now abandoned).

It is known that zinc oxide can be employed in making photoconductive layers which can be coated on ordinary paper, and that photographic copies can be conveniently prepared from these photoconductive materials. This process is somewhat related to the system known as xerography, in that a photoconductive element is given a uniform charge, usually from a corona discharge, followed by exposure to an image using radiation to which the photoconductive composition is sensitive. This exposure causes an imagewise discharge of the charge on the surface of the photoconductive composition (the electrostatic charge leaking away from the surface roughly in proportion to the amount of radiation received, as describedbelow), so that the portions of the surface retaining their charge can then be treated with a charged powder or toner of opposite charge. This powder or toner is attracted to the portions of the surface retaining a charge, thus giving a visible copy which may be fixed in a number of various ways to the surface, or alternatively, transferred to another sheet or surface which provides the permanent copy.

In the known system of employing zinc oxide in photoconductive layers, a relatively conducting support, such as paper, is coated with a photoconductive zinc oxide dispersed in an electrically insulating binder material. The grounded support is then placed beneath a corona discharge so that a blanket negative electrostatic charge on the Zinc oxide surface is accumulated. Inasmuch as the zinc oxide is a photoconductive material, it is necessary to perform this charging separation in the substantial absence of any ultra-violet or visible radiation. The charged zinc oxide photoconductive layer can then be exposed to a photographic image in the usual manner, the portions of the zinc oxide which receive light or ultra-violet radiation losing wholly or in part (depending upon the extent of exposure), the negative electrostatic charge, while the unexposed or partially exposed portions of the charged layer retaining their negative electrostatic charge. The resulting latent image can then be developed to a visible image by means of a pigment powder which has a charge opposite to the negative charge remaining on the areas of the photoconductive layer. The pigment powder is thus strongly attracted to the negatively charged areas and can be permanently affixed to the surface of the photoconductive layer by simply melting the vehicle for the powder at some temperature below the charring temperature of the paper support.

One of the disadvantages of the zinc oxide normally used in photoconductive layers is that the sensitivity is not primarily within the visible region of the spectrum, so that such materials have a relatively low speed when an ordinary light source, such as a tungsten lamp or fluorescent lamp, is used as the exposing source. The zinc oxide normally employed in such photoconductive layers has its greatest sensitivity in the ultra-violet region of the spectrum, and normal light sources have "ice very weak radiation in this region. While various sensitizing materials have been suggested to increase the sensitivity of zinc oxide in the visible region of the spectrum, so that the zinc oxide has some panchromatic or orthochromatic sensitivity, many of these dyes are unsatisfactory since they must be used in such large amounts to obtain optimum sensitivity that the surface of the paper takes on a very strong coloration which reduces the contrast of the desired image and has an-undesirable esthetic effect. For example, it has been previously suggested to use organic dyes such as Rose Bengal to increase the sensitivity of the zinc oxide,-but this material has a very strong coloration so that the nude sirable effects mentioned above are quite evident.

It is, therefore, desirable to have a means of increasing the sensitivity of zinc compositions to conventional light sources, such as tungsten light, without seriously affecting the coloration of the photoconductive surface. Moreover, it is desired to have more effective sensitizing means so that shorter exposure times can be employed in the reproduction of graphic originals. It is also desired to have zinc oxide photoconductive compositions which have sensitivity to particular wavelengths of radiation, so that the photoconductive compositions'can be used in the manufacture of color materials.

An object of our invention is to provide a convenient means of increasing the sensitivity of photoconductive zinc oxide layers to visible radiation. Another object is to provide photoconductive zinc oxide layers which have much higher speeds than those previously available.

Still another object is to provide a means for sensitizingphotoconductive zinc oxide compositions to particular regions of the spectrum so that these compositionscan be used in the manufacture of color materials. Other objects will become apparent from a consideration of the followa ing description and examples;

The following invention relates to the discovery that certain polymethine dyes containing a mercapto group can be used to usefully extend the sensitivity of photoconductive zinc oxide compositions. The polymethine dyes of our invention conveniently contain a cyclic.

positions, they have not found wide use in the photo-v graphic field because of their relatively poor sensitizing action for silver halides. It 'was, therefore, unexpected to find that such dyes could be used to extend the sensitivity of zinc oxide to an extent many. times that obtainable with more conventional spectral sensitizing dyes, such as the N-substituted merocyanine dyes.

The effect of our new dyes on photoconductive zinc oxide compositions is graphically shown in the accompanying drawings wherein the curves in FIGURES 1-3 represent the sensitivity of photoconductive zinc oxide compositions sensitized with polymethine dyes according to our invention. Further details regarding such sensitizing action are given below.

The polymethine dyes which can be usefully employed according to our invention comprise many of the wellknown classes of sensitizing dyes which have been used in silver ialide photography, and they include dyes containing a cyclic ketomethylene acidic nucleus. Such dyes It has been found that dyes containing a subinclude simple merocyanine dyes, merocarbocyanine dyes, merodicarbocyanine dyes, trinuclear holopolar dyes, complex merocyanine dyes, etc. Many of the useful dyes of our invention contain a H l N .C

group as a part of the ketomethylene acidic nucleus. It is apparent that these dyes can readily enolize to structures containing a mercapto group.

Polyrnethine dyes of the merocyanine class which can be usefully employed in our invention include those dyes represented by the following general formula:

a R1 R-NZ GH=OH),. :C(=H0H) r(=0Hc)m ,=C 0=0 wherein R represents an alkyl radical, Le, a substituted or unsubstituted alkyl group, such as methyl, ethyl, n-propyl, n-butyl, isobutyl, n-amyl, isoamyl, fl-methoxyethyl, p-ethoxyethyl, carboxymethyl, etc. (especially an alkyl group containing from 1 to 4 carbon atoms, R represents a hydrogen atom or an alkyl group, such as methyl, ethyl, etc, d, m and 11 each represents a positive integer of from 1 to 2, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus of the type common in cyanine dye chemistry, such as those selected from the group consisting of a thiazole nucleus (e.g., thi-azole, 4-methylthiazole, 4-phenylthiazole, S-methylthiazcle, S-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthi azole, 5-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 4-(2-thienyl)thiazole, etc), a benzothiazole nucleus (e.g., benzothiazole, 4-chlorobenzothiazole, S-chlorobenzothiazole, 6-chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzcthiazole, S-methylbenzothiazole, 6-methylbenzothiazole, S-bromcbenzothiazole, 6 bromobenzothiazole, 4 phenylbenzothiazole, 5-phenylbenzothiazole, 4-methoxybenzo thiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole, S-iodobenzothiazole, 6 iodobenzothi azole, 4 ethoxybenzothiazole, S-ethoxybenzothiazole, tetrahydrobenzothiazole, 5,6-dimethoxybenzothiazole, 5,6-dioxymethylenebenzothiazole, S-hydroxybenzothiazole, 6-hydroxybenzo'thiazole, etc), a naphthothi azole nucleus (e.g., naphtho[l,2]thiazole, naphtho[2,l]thiazole, 5 methoxynaphtho[2,l]thiaz0le, S-ethoxynaphtho[2,l1thiazole, 8 methoxynaphtho[1,2]- thiazole, 7-methoxynaphtho[1,2]thiazole, etc), a thianaphtheno-7,6',4,5-thiazole nucleus (e.g., 4-methoxythianaphtheno-7',6,4,5-thiazole, etc), an oxazole nucleus (e.g., 4-methylcxazole, S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole, 4,5-dirnethyloxazole, 5-phenyloxazole, etc), a benzoxazole nucleus (e.g., benzoxazole, S-chlorobenzoxazole, S-methylbenzoxazole, 5-phenylbenzox azole, 6-methylbenzoxazole, 5,6- di-methylbenzoxazole, 4,6-dimethylbenzoxazole, S-me-thoxybenzoxazole, 5-ethoxybenzoxazole, S-chlorobenzoxazole, 6 methoxybenzoxazole, 5 hydroxybenzoxazo-le, 6-hydroxybenzoX-azole, etc), a naphthoxazole nucleus (e.g., naphtho[l,2]oxazole, naphtho[2,l]oxazole, etc), a selenazole nucleus (e.g., 4-methylselenazo1e, 4-phenylselenazole, etc), a benzoselenazole nucleus (e.g., benzoselenazole, S-chlorobenzoselenazole, 5 -methoxybenzoselenazole, S-hydroxybenzoselenazole, tetrahydrobenzoselenazole, etc), a naphthoselenazole nucleus (e.g., naphtho[l,2]selenazole, naphtho[2,l]selenazole, etc), a thiazoline nucleus (e.g., thiazoline, 4-methylthiazoline,

etc), a Z-quinoline nucleus (e.g., quinoline, 3-methylquinol-ine, S-methylquinoline, 7-methylquinoline, 8-methylquinoline, 6 chloroquinoline, 8 chloroquinoline, 6-methoxyquinoline, 6-ethoxyquinoline, 6-hydroxyquinoline, 8-hydroxyquinoline, etc), a 4-quinoline nucleus (e.g., quinoline, 6-methoxyquinoline, 7-methylquinoline, 8-methylquinoline, etc), a l-isoquinoline nucleus (e.g., isoquinoline, 3,4-dihydroisoquincline, etc), a benzimidazole nucleus (e.g., 1,3-diethylbenzimidazcle, l-ethyl-3- phenylbenzrirnidazole, etc), a 3,3-dialkylindolenine nucleus (e.g., 3,3-dirnethylindolenine, 3,3,5-trimethylind0- lenine, 3,3,7-=trimethylindolenine, etc), a 2-pyridine nucleus (e.g., pyridine, S-methylpyridine, etc), a 4-pyridine nucleus (e.g., pyridine, etc), etc, and Q represents the nonsrnetallic atoms necessary to complete an acidic heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, provided said latter heterocyclic ring contains an enolizable s H II N group. Particularly useful merocyanine dyes embraced by Formula I above include those dyes represented by the following general formula:

I'M O=C1 |TR2 (-cH=oH) r1 0 (=CHCH) (=CHO)m-r=C o=s H I 0 RH group, wherein R and R" each represents a hydrogen atom, an alkyl group, such as methyl, ethyl, n-propyl, n-butyl, n-hep-tyl, n-octyl, etc. (e.g., an alkyl group containing from 1 to 8 carbon atoms), or an aryl group, such as phenyl, 0-, -m-, and p-tolyl, etc, providing that at least one of the members selected from the group consisting of R R and R is a hydrogen atom, i.e., such compounds as defined by Formula Ia must contain an enolizable thiocarbamido group as defined above.

Another group of polymethine dyes which can be usefully employed in our invention include those dyes represented by the following general formula:

wherein R, R X, n, d and Z have the values given above and Z represents the atoms necessary to complete a cyclohexene ring, which may contain simple substituents, such as alkyl groups (e.g., methyl, ethyl, etc).

Another group of polymethine dyes which can be usefully employed in our invention is the class of dyes represented by the following general formula:

5 6 wherein R, R X, n, d and Z each have the values given above, R represents an alkyl radical, including substis =C-NH tu ted or unsubstituted alkyl groups, such as those defined by R above, p represents a positive integer of from 1 t0 2 CH CH K S and Z represents the non-metallic atoms necessary to 5 complete a heterocyclic nucleus containing from 5 to 6 I atoms in the heterocyclic ring of the type commonly 5 employed in cyanine dye chemistry, such as are defined by Z above.

The polymethine dyes represented by Formulas Ia and 10 O o=c 1m Ib above have been written in their keto form. It is to I r be understood, however, that dyes of'this type, and also l C CH CH C N C the dyes of Formula 10 can be written in their enol form. N H For instance, the dyes of Formula Ia can alternatively be written in the following form: C 3

\ a l l X c on on c c s \s/ wherein R, R X, n, d, m and Z each have the values N given above. e

The merocyanine dyes embraced by our invention can 3 be prepared according to techniques which have been previously described in the prior art. Among such pat- (5) ents describing methods for making such dyes are the (c1 1 following: C NH I 1 Brooker et al. US. Patent 2,161,331, granted June 6, 1939 C CH CE K S Brooker US. Patent 2,170,803, granted August 29, 1939 H Brooker U.S. Patent 2,170,804, granted August 29, 1939 Brooker US. Patent 2,170,807, granted August 29, 1939 3 Brooker US. Patent 2,177,401, granted October 24, 1939 y Brooker US. Patent 2,177,403, granted October 24, 1939 (6) As shown by the above formulas, the polymethine 0 J chain in our dyes can contain conventional substituents. CH CH: C c 5 Methods for making such dyes have been previously de- N scribed in the prior art. See, for example, Brooker and 4 N H White U.S. Patent 2,263,757, issued November 25, 1941, H and Kendall and Collins US. Patent 2,319,547, issued 2 5 May 18, 1943. 7

The merocyanine dyes of Formula Ib can be prepared according to methods which have been previously de- 07C scribed in the prior art. See, for example, Brooker and C CH CH Heseltine U.S. Patent 2,856,404, issued October 14, 1958.

The holopolar dyes of Formula R can be prepared 1 according to methods previously described in the prior 6 5 art. See, for example, Brooker and White Reissue US. 2H5 Patent 24,292, reissued March 19, 1957 (original Patent No. 2,739,964, issued March 27, 1956). (8)

Trinuclear and complex merocyanine dyes which can 0 o=c 2 5 be usefully employed in our invention have also been 8 CH CE S described in the patent literature. For example, Fry and 551 l Kendall US. Patent 2,388,963, issued November 13, 1945, H describes a method of making complex merocyanine dyes which can be usefully employed in our invention. (See 5 Example 18, for instance.) Heseltine and Brooker US.

Patent 2,719,151, issued September 27, 1955, describes 603(9) the preparation of trinuclear merocyanine dyes which 5 o=c N 3 can be used in our invention. (See, for instance, Examr r P1621) Q C=CH-CH=C\ /C=S Typical polymethine dyes which can be employed in g practicing our invention include the following: 1 l

3 10) C NH S 0=C NH 0\ 21 4 3 S CH CH 0 (3* S /C S o. N N I I c n E, ,1 e 3 dye can be added to the zinc oxide composition while disi solved in an organic solvent. Pyridine, methanol, ethanol, acetone, etc, can be used to dissolve many of the dyes useful in practicing our invention. The zinc oxide can be uniformly dispersed in an organic solution of the binder customarily employed for the zinc oxide and a solution of the sensitizing dye added to this coating solution. After thorough mixing, the sensitized composition can be coated on a paper support and dried in the usual manner.

Alternatively, an unsensitized zinc oxide coating can be prepared as described above and after removal of the organic solvent, the-paper coating can be immersed in a solution of the sensitizing dye. This method has been found to be particularly useful in that higher speeds can be frequently obtained.

The binders for the zinc oxide comprise many of the resinous compositions which are commercially available. Such resins are sold under trade names, such as Plaskon ST-856, Rezyl 405-18, Pliolite S7 or S-SD, Styresol 4440, DC 804, etc. These resins comprise styrene-butadiene copolymers, silicone resins, styrene-alkyl resins, silicone-alkyd resins, soya-alkyd resins, polyvinyl chloride, polyvinyl acetate, etc. The methods of making such resins have been previously described in the prior art. For example, styrene-alkyd resins can be prepared according to the method described in Gerhart US. Patent 2,361,019, issued October 24, 1944; Rust US. Patent 2,258,423, issued October 7, 1941; Kropa US. Patent 2,453,665, issued November 9, 1948, etc. Other binders, such as paraffin, mineral waxes, etc., can also be employed. These binders are generally characterized as having marked hydrophobic properties (i.e., being substantially free of any water-solubilizing groups, such as hydroxyl, free acid groups, amide groups, etc.) and as being good electrical insulators or as having high electrical resistivity. These binders can be easily dissolved in organic solvents having a boiling point below the charring temperature of the paper support. Also, these binders have the desirable property of readily dispersing the zinc oxide photoconductive material. Some resinous binders are relatively poor insulators and do not provide coatings which can be stored for prolonged periods of time after the photoconductive coatings have been negatively charged. This is particularly noticeable at relatively high humidities, and the photoconductive coatings should be charged shortly before use in such instances, that is, it is not advisable to charge the photoconductive coatings too long in advance before use. Such problems are well understood by those skilled in the art.

Non-polar solvents have been found to be particularly useful in preparing the photoconductive layers in that any residual solvent which cannot be removed does not have a deleterious effect on the keeping qualities of'the photoconductive layers. Such solvents include the aromatic hydrocarbons, such as benzene, xylenes, toluene, etc;

The zinc oxide employed in our invention should generally consist of relatively small particles of less than 0.5 micron mean diameter. Such zinc oxide materials are readily available and can be purchased under a variety of trade names, such as Protox No. 168 (New Jersey Zinc Company), etc. Sufficient binder should be employed to insulate each of the zinc oxide particles from the surrounding particles in the composition. The most useful or optimum quantity of zinc oxide to binder for a particular binder can be readily determined by making a series of test coatings wherein the quantity and relative amounts of zinc oxide to binder are employed.

Exposure of the charged photoconductive layer to visible radiation or ultraviolet radiation causes a loss or reduction of the negative charge in those portions of the photoconductive material which are exposed to the radiation. The degree of loss will dependon the intensity and time of exposure to the radiation, in general. The resulting latent electrophotographic image can then be developed to a visible image in a variety of ways, including those which have been previously employed in electrophotographic processes, such as xerography. A particularly useful means of developing the latent electrophotographic image comprises use of a magnetic brush. This magnetic brush development makes use of a ferromagnetic powder, such as iron filings, which has been intimately mixed with pigmented resin, or sulfur. Agitation of the ferromagnetic powder and pigmented resin results in a triboelectric effect wherein the pigmented resin acquires an electric charge depending upon the relative position of the resin to the ferromagnetic powder in the triboelectric series. That is, ordinary iron powder is below most resins in the triboelectric series, and mixture with a resin higher in the series results in the deposition of a positive electrostatic charge on the resin; The result ing mixture can then be picked up by a magnet on which the iron particles, or other ferromagnetic powder, arrange themselves in the conventional pattern, so that the long chains of filings resemble an ordinary brush; This magnetic brush can then be placedin contact with the exposed photoconductive layer and the brush passed across the negative electrostatic latent image whichis on the surface of the photoconductive material. As the magnetic brush passes over the areas of the photoconductive material which have residual negative charge thereon, the electrosatic attraction between the charged pigmented resin particles and the oppositely charged image areas in the photoconductive material is greater than the attraction between these particles and the ferromagnetic powder, so that the pigmented resin is deposited on the surface of the photoconductive material roughly in proportion to the residual charge on the surface of the photoconductive layer. By selecting a resin with a low melting point, the developed image can then be fixed to the surface of the paper by heating to a temperature above the meltingpoint of the resin, but below the charring temperature of the paper. The resin in the pigmented resin compositions can be varied, depending upon the effects desired and the type of copy which is being reproduced. Such resins may be the same as those employed in the insulating layer coated on .thepaper support, such as .styrene-butadiene resins, etc. The particle size of the pigmented resin used in development can vary, although the range of 0.1 to 25 microns is adequate for most purposes. Various pigments can be used in the resin developing compositions. The ability of the pigmented resin charge is dependent upon the type of resin selected. The pigment merely serves to impart color to the resin and probably imparts very little, if any, influence on the overall charge of the pigmented resin.

The following examples will serve to illustrate the manner of using the optically sensitizing photoconductive materials of our invention.

A series of dyes represented by the above numbers were dissolved in a suitable solvent, such as acetone, py-

ridine, methanol, etc., depending upon the solubility characteristics of the particular dye, and separate sheets of paper coated with unsensitized zinc oxide compositions were immersed for about 15' seconds in these solutions containing the sensitizing dyes. The sensitizing zinc oxide papers were then dried in air in a vertical position. After drying, the paper strips were exposed to a 10,000- volt corona discharge for 15 seconds and then exposed to tungsten illumination for 2 seconds in an intensity scale sensitometer and spectrograph. The exposed coatings were then developed by the magnetic brush technique described above using small iron particles dispersed in black pigmented sulfur. Finally, the images were fixed by fusing the developed image to the paper at a temperature of about the same manner with the sensitizing dye being omitted from the sensitizing solution. This served as a control, the speed of which was arbitrarily set at one. In the following table the dyes are identified by number and in terms of their concentration in the sensitizing solution.

to accept a positive C. A duplicate strip was .treated' in 1 l The relative speed, as compared to the control, sensitizing maximum and range, are also given.

Table Relative sensitizing Data Cone. White Dye (Percent) Light Speed Max. Ran e 1 .01 4 430 to 470 002 2 520 480-540 .01 4 480 to 520 .01 16 540 to 580 .01 4 520 to 560 .1 3 480 .01 g 500 450-530 .1 l 3 to 680 .01 16 530 to 600 01 8 490 to 550 01 32 580 to 680 .01 32 580 to 680 .01 8 680 580-690 .01 2. 8 480 to 520 01 8 01 16 520 440-540 01 8 580 460-620 .01 4 600 520-630 .01 8 640 580-680 .01 8 600 500-680 .01 8 620 520-680 01 16 500, 610 430-630 'Ihe accompany drawing will serve to illustrate schematically the effect of our polymethine dyes in extending the sensitivity of photoconductive zinc oxide compositions.

In FIGURE 1, the solid curve represents the sensitivity of zinc oxide, sensitized with -[(l,3,3t1imethyl-2(1H)- indoleninylidene)ethylidene]rhodanine. The sensitizing data for this dye are given in the above table, dye 4.

In FIGURE 2, the solid curve represents the sensitivity of a photoconductive zinc oxide sensitized with 5 [(3-ethyl-2 (3H) -benzoxazolylidene)ethylidene] 1- phenyl-Z-thiohydantoin. The sensitizing data for this dye are given in the above table, dye 7.

In FIGURE 3, the solid curve represents the sensitivity of a photoconductive zinc oxide material sensitized with 5 (3 ethyl 2(3H)-benzothiazolylidene)ethylideneJ- l-methyl-Z-thiobarbituric acid. The sensitizing data for this dye are given in the above table, dye 17.

-It has also been found that the sensitizing dyes of our invention can be usefully employed to extend the sensitivity of zinc oxide material intended for use in a photoconductographic process. Photoconductographic processes have been previously described in the prior art, such as in Bronk British Patent 188,030, accepted October 23, 1922, and Hana Dutch Patent 5,142, patented June 13, 1920.

The following examples will serve to illustrate the method of using the sensitized zinc oxide compositions of our invention in a photoconductographic process.

Dyes 17, 22 and 23 were separately dissolved in a suitable solvent and mixed with a composition comprising photoconductive zinc oxide and a resinous, insulatorbinder comprising a synthetic resin, such as Pliolite 8-7 (a styrene butadiene copolymer), the concentration of the dyes being 5.6 micromoles per 56 grams of zinc oxide. The zinc oxide to binder ratio was 3:1. A solvent mixture comprising 95% toluene and 5% methanol was added to give a mixture containing 35% solids by weight, and the solutions were separately coated at a thickness of 0.010 inch, wet, on paperabacked aluminum foil.

Each of the coatings was then dried and exposed in the customary manner to daylight-quality radiation in a high intensity wedge spectrograph. The exposed coatings were then developed by contacting the exposed surfaces with a viscose sponge wet with a developer solution comprising sodium thiosulfate saturated with silver chloride. The viscose sponge was held .at a potential of about 70 volts positive with respect to the aluminum foil backing. The sensitizing data for each of the coatings was approximately the same as indicated in the above table for coatings obtained in an electrophotographic process. For example, dye 17 gave a sensitizing maximum of about 520 with sensitivity extending from about 440 to 540 m The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim as our invention and desire secured by Letters Patent of the United States is:

l. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a merocyanine dye selected from the class represented by the following general formula:

wherein R represents an alkyl group containing from 1 to 4 carbon atoms, R represents a member selected from the class consisting of a hydrogen atom and an alkyl group containing from 1 to 2 carbon atoms, d and m each represents a positive integer of from 1 to 2, R represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 4 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

group and a group, wherein R and R" each represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the class consisting of R R and R" is a hydrogen atom, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the class consisting of a thiazole nucleus, a benzothiazole nucleus, a naphtho thiazole nucleus, a thianaphtheno-7',6,4,5-thiazole nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, a thiazoline nucleus, a 2-quinoline nucleus, a 4-quinoline nucleus, a l-isoquinoline nucleus, a benzimidazole nucleus, a 3,3- dialkylindolenine nucleus, a Z-pyridine nucleus and a 4-pyridine nucleus, and n represents 1 when Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing 5 atoms in the heterocyelic ring and n represents a positive integer of from 1 to 2 when Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of a 2-quinoline nucleus, a 4-quinoline nucleus, a l-isoquinoline nucleus, a 2-pyridine nucleus and a 4-pyridine nucleus.

2. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a merocyanine dye selected from the class represented by the following general formula:

13 wherein R represents an alkyl group containing from 1 to 4 carbon atoms, a represents a positive integer of from 1 to 2, Z represents the atoms necessary to complete a cyclohexene ring, R represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 4 carbon'atoms and an aryl group containing from 6 to 7 carbon atoms, X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

group and 'a group,. wherein ,R' and R? each represents a member selected from the class=consistirrg of a hydrogen atom, an alkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the classconsisting of R R, and R is a hydrogen atom, Z represents the non-metallic atoms necessary to complete a heterocyclic-nucleus selected from theclass consisting of a thiazole nucleus, 21 benzothiazole nucleus, a naphthothiazole nucleus, a thianaphtheno-7,6',4,5-thiazole nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, a thiazoline nucleus, at 2-quinoline nucleus, a 4-quinoline nucleus, 21 l-isoquinoline nucleus, a benzimidazole nucleus, a 3,3-dialkylindolenine nucleus, at Z-pyridine nucleus and a 4-pyridine nucleus, and n represents 1 when Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing atoms in the heterocyclic ring and n represents a positive integer of from 1 to 2 when Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of a Z-quinoline nucleus, a 4-quinoline nucleus, a l-isoalkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the class consisting of R R and R is a hydrogen atom, Z and Z each represents the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the class consisting of a thiazole nucleus, a benzothiazole nucleus, a naphthothiazole nucleus, a thianaphtheno-7,6',4,5- thiazole nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, a thiazoline nucleus, a 2-quinoline nucleus, a 4-quinoline nucleus, a l-isoquinoline nucleus, a benzimidazole nucleus, a 3,3-dialkylindolenine nucleus, a 2-pyridine nucleus and 4-pyridine nucleus, and n and p represent 1 when Z and Z represent the non-metallic atoms necessary to complete a heterocyclic nucleus containing 5 atoms in the heterocyclic ring and n and 1, respectively each represent a positive integer of from 1 to 2 when Z and Z each represent the non-metallic atoms necessary to complete a heterocyclic nucleus selected from the group consisting of a 2-quinoline nucleus, a 4-quinoline nucleus, at l-isoquinoline nucleus, a Z-pyridine nucleus and a 4-pyridine nucleus.

4. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a merocyanine dye selected from the class represented by the following general formula:

wherein R represents an alkyl group containing from 1 to 4 carbon atoms, R represents a member selected from the class consisting of a hydrogen atom and an alkyl group containing from 1 to 2 carbon atoms, a! and In each represents a positive integer of from 1 to 2, R represents 2332 1 5 nucleus a 2 Pyudme nucleus and a 4 pyndme 40 a member selected from the class consisting of a hydro- 3. A photoconductive composition comprising sensigen atom an alkyl group i i from 1 to 4 carbon tized photoconductive zinc oxide particles uniformly disatoms gz an i i 2312 225 35? 5 z g fsg persed in a high dielectric, organic binder-insulating a 5 i Z 3 Sulfur atom c S material for saidzinc oxide, said zincoxide being sensi- Comm 0 an O yge a tized with a holopolar dye selected from the class rep- T resented by the following general formula:

."'Z--- R I NZ -on=on n 1 o=cn-( =on-orr d r=on-oZ oH--o1r N --R,

\\ N-m C H S wherein R and R each represents an alkyl group containgroup and a ing from 1 to 4 carbon atoms, d represents a positive integer of from 1 to 2, R represents a member selected ll l from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 4 carbon atoms and an aryl group containing from 6 to ,7 carbon atoms, X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

group and a II I 0 RI! group, wherein R and R" each represents a member selected from the class consisting of a hydrogen atom, an

6. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a merocyanine dye selected from the class represented by the following general formula:

wherein R represents a member selected from the class consisting of an alkyl group containing from 1 to 4 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, R represents a member selected from the class consisting of a hydrogen atom and an alkyl group containing from 1 to 2 carbon atoms, d and In each represents a positive integer of from 1 to 2, R represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 4 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

group and a II I group, wherein R and R" each represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the class consisting of R R and R is a hydrogen atom, and Z represents the non-metallic atoms necessary to complete a 3,3-dialkylindolenine nucleus.

7. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a dye represented by the following formula:

8. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said Zinc oxide, said zinc oxide being sensitized with a merocyanine dye selected from the class represented by the following general formula:

wherein R represents an alkyl group containing from- 1 to 4 carbon atoms, R represents a member selected from the class consisting of a hydrogen atom and an alkyl group containing from 1 to 2 carbon atoms, d and m each represents a positive integer of from 1 to 2, R

16 represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 4 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

group anda ll 1's" group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the class consisting of R R and R" is a hydrogen atom, and Z represents the non-metallic atoms necessary to complete a benzothiazole nucleus.

9. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a dye represented by the following formula:

0 on s I 10. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a merocyanine dye selected from the class represented by the following general formula:

/Z\ H2O CHzO=CIIT-Rz R-N C='CH(CH=CH)d1C 0:0 o=s o X H group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the class consisting of R R and R is a hydrogen atom, and Z represents the non-metallic atoms necessary to complete a benzoxazole nucleus.

11. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dis persed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a dye represented by the following formula:

12. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a holopolar dye selected from the class represented by the following general formula:

group wherein R and R" each represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the class consisting of R R' and R represents a hydrogen atom, and Z and Z each represents the non-metallic atoms necessary to complete a naphthot-hiazole nucleus.

13. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a dye represented by the following formula:

References Cited in the file of this patent UNITED STATES PATENTS 2,078,233 Brooker Apr. 27, 1937 2,177,403 Brooker Oct. 24, 1939 2,734,900 Heseltine Feb. 14, 1956 FOREIGN PATENTS 201,416 Australia Apr. 13, 1956 OTHER REFERENCES CA, 43, 7349d (1949). (Copy in Sci. Lib.)

Mees: The Theory of the Photographic Process, revised edition (1954), pages 430-500.

Nelson: Journal of the Optical Society of America, 46 (No. 1),]anuary 1956, pp. 13-16.

Young et al.: R.C.A. Review, December 1954, pages 469-484. 

1. A PHOTOCONDUCTIVE COMPOSITION COMPRISING SENSITIZED PHOTOCONDUCTIVE ZINC OXIDE PARTICLES UNIFORMLY DISPERSED IN A HIGH DIELECTRIC, ORGANIC BINDER-INSULATING MATERIAL FOR SAID ZINC OXIDE, SAID ZINC OXIDE BEING SENSITIZED WITH A MEROCYANINE DYE SELECTED FROM THE CLASS REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 